The present disclosure generally relates to a control system and method for an internal combustion engine, and more particularly to a control system and method that includes modifying a throttle return trigger point during a transmission upshift when retard control of the internal combustion engine is disabled.
It is known to modify engine ignition timing and throttle position, at least temporarily, in order to reduce engine power during clutch to clutch up-shifting in an automatic transmission. Reducing engine power by modifying ignition timing is often referred to as “engine retard control.” It also known that engine retard control may be disabled during certain vehicle operating conditions, such as during engine warm-up (e.g., from cold temperatures). When engine retard control is disabled, clutch to clutch up-shifting typically progresses more slowly and a normal throttle return trigger point may be inappropriate. (i.e., not appropriate relative to the progress of the up-shift).
More particularly, the throttle position is typically modified by moving the throttle from an initial position to a more closed position until a certain gear ratio threshold value is reached. Reaching of the gear ratio threshold value can be referred to as the throttle return trigger point because the throttle is moved back to the initial position from the more closed position when the gear ratio threshold value is reached. The gear ratio threshold value, and thus the throttle return trigger point, is set to correspond to an expected duration of the up-shift such that the throttle returns to its initial position near the end of the up-shift which results in good feeling to the vehicle operator and low clutch heat. When engine retard control is disabled, however, the shift progresses more slowly and the gear ratio threshold value (i.e., the throttle return trigger point) no longer accurately corresponds to the duration of the up-shift. As a result, the throttle moves from the more closed position back to the initial position in the middle of the up-shift and results in poor feeling to the vehicle operator and high clutch heat.